DE 41 08 028 A1 already reveals a brake pressure control comprising a hydraulically actuable slide valve integrated into the valve accommodating body to absorb the valve switching noises during the electromagnetic actuation of the inlet and outlet valves. For this purpose, the slide valve is provided with a blind bore arranged within a annular groove on the slide valve which is operative within a pressure fluid area connecting the pressure fluid source to the inlet valve. The webs of the annular groove form the control edges confining the volume flow as soon as the slide valve leaves the basic position determined by a compression spring. Finally, another annular groove provided on the slide valve establishes the connection to the inlet valve hydraulically opened in the basic position.
It has been found that during the hydraulic actuation of the slide valve leakage flows cannot be prevented from occurring on the metallically sealed area of the cylindrical face, that are likely to result in an undesired pressure increase ahead of the inlet valve as long as the same is closed. Accordingly, during opening of the inlet valve, a substantial pressure prevails exerting an unfavorable effect on the noise pattern.
JP-A-61-6055 discloses a brake pressure control comprising a slide valve provided in the pressure fluid connection between a brake pressure generator and an inlet valve controlling the brake pressure toward the wheel brake. On both front faces of the slide valve, the wheel brake pressure determined by the brake pressure generator prevails in the open switching position of the inlet valve. In a non-locking brake pressure control phase in which the inlet valve separates the pressure fluid connection between the brake pressure generator and the wheel brake (and in which the outlet valve coupled to the inlet valve causes a pressure decrease by opening a pressure fluid connection to a pressure fluid accumulator), a pressure different develops at both front sides of the slide valve which moves the slide valve in its locking position, thereby separating the brake pressure generator from the hydraulic system coupled thereto.
The locking position of the slide valve is caused by a conical ceiling seat on the slide valve. Leakage from the metallically sealed conical sealing face cannot be prevented from occurring. The leakage flow is likely to result in an undesired pressure increase ahead of the closed inlet valve.
A slide valve for a brake pressure control exclusively comprising a metallic ceiling of the cylindrical surface thereof within its housing, its taught by JP-A-63-78856. Between the two front faces of the slide valve, the shaft is provided with a circular grove which with the control edge thereof determines the pressure fluid intake from the brake pressure generator to the wheel brake. One of the front faces is exposed to the pressure of the brake pressure generator whereas the other front face in response to the hydraulically actuated position of the inlet valve is exposed to either the pressure of the brake pressure generator or to the controlled pressure within the wheel brake. The slide valve separates the brake pressure generator from the connect wheel brake as soon as the pressure within the wheel brake is decreased in a non-locking control. This separation takes place because the pressure proportional to the pedal force (which prevails on the opposite front side of the slide valve) produces a pressure difference which is operative to actuate the slide valve. Due to the exclusive metallic ceiling of the slide valve in the housing, leakage from the metallically sealed cylindrical surface cannot be prevented. Such leakage is likely to result in an undesired build-up of pressure fluid in the direction of the hydraulically actuated inlet valve during the non-locking control thereof.
Both JP-A-63-78856 and JP-A-61-6055 disclose hydraulically actuated separating valves which during a non-locking actuation of the brake remain in a deenergized condition in their basic position. No control of the pressure fluid volume supplied by the brake pressure generator to the wheel brake is provided.
It is therefore an object of the invention to overcome the afore-mentioned disadvantages by performing as few structural changes in the brake pressure control as possible thereby efficiently reducing, and all operating conditions, the valve switching noises.
This invention accomplishes these objectives by employing the principle of preventing leakage by suitably arranging pressure fluid channels and sealing elements and by specifically guiding the flow of pressure fluid.